1. Field of the Invention
The present invention relates to a method and apparatus for repairing and testing synchronous motors and to a synchronous motor exciter control circuit tester hereinafter referred to as synch circuit tester which will simulate a synchronous motor approaching, reaching, and passing the point at which it locks onto its particular synchronous speed.
2. Description of the Prior Art
Many synchronous motors, especially those using brushless excitation are equipped with exciter control circuits which are used to develop and control the DC power necessary to realize synchronous operation. One such exciter control circuit as shown in FIG. 4 includes a three-phase rectifier connected to a three-phase power source (which is rectified to provide DC voltage), a pair of silicon controlled rectifiers 8 and 12 with respective control assembly circuits 10 and 14, a diode 16, and a field discharge resistor 18 which are operably connected to the main DC field winding of the motor 20. A more detailed description of such a device is given in U.S. Pat. No. 3,100,279, Control System For Controlling The Operation of Synchronous Motors which issued on Aug. 6, 1963 to T. G. Rohner.
In many cases, the control circuit components are installed on a mounting ring. The mounting ring is mounted to the motor rotor of the synchronous motor. Therefore, the control circuit components rotate on the rotor and are not accessible during motor operation. Each control circuit is capable of a wide range of rotor speeds over which it will try to lock the rotor onto a fixed speed. However, if the control circuit operates before or after a motor's particular rotor speed, the motor will not lock onto its synchronous speed and it becomes necessary to repair the exciter control circuit.
In the past, the adjustment of the control circuit has been accomplished using a field trial-and-error method, resulting in uncertainty of operation associated with an untested repair and blind adjustment of the control circuit operating point.
It has been determined, in view of the pitfalls of the past trial and error methods, that a much better operation of the motor may be obtained if the mounting ring with the defective control circuits is removed from the motor and replaced with a new mounting ring with an accurately functioning control circuit which has already been accurately bench tested for proper operation or alternatively, removed from the motor, repaired and then reinstalled in the motor. However, the standard mounting ring for the motor is continuously formed (i.e., donut shaped) around the rotor shaft and therefore requires the removal of the end bearing of the motor and other major mechanical work before it can be removed from the shaft of the motor. Thus, the removal of the standard mounting ring and the replacement thereof normally requires at least one work day. This down time of the motor being totally unacceptable, it was necessary to develop a means for quick and easy removal and replacement of the mounting ring.
Previously no device was available to satisfactorily simulate the operation of the motor so that the control circuit on the mounting ring could be tested without attaching the mounting ring to the motor and commencing actual operation thereof.
The present invention overcomes the aforesaid problems and deficiencies associated with the prior art repair methods by providing an easily replaceable sectioned mounting ring, a method of testing and repair and a synch circuit tester which enables adjustment of the synchronous motor exciter control circuit without actual operation of the synchronous motor and also facilitates detection of any malfunctioning components in the synchronous motor exciter control circuit.